88 MR. II. CHARLTON BASTIAN'S MONOGRAPH 



sprouting from the licaltliy seed, and then insert themselves between the sheaths of its 

 leaves, gradually working their way round till they come to the innermost of these, where 

 they remain for a variable time, without increasing much in size, till the rudiment of the 

 future ear begins to form. The length of time during Avhich they remain in this situa- 

 tion, and their degree of activity, depend upon the rapidity of growth of the plant 

 and the moisture of the season. The remainder of the process may be best described in 

 Davaine's own words; he says: — " L'epi du ble, avant de parattre au dehors, se forme 

 et reste longtemps renfermc dans les gaines des dernieres feuillcs. Les auguillules, 

 libres dans ces gaines, le rencontrent et peuvent s'introduire entre les parties qui le 

 composent. Pour que I'invasion des an^guillules soit suivie de la production de la 

 nielle, il faut que la rencontre ait lieu a une epoque tres-rapprochee de la formation de 

 l'epi. Lorsque celui-ci n'a encore que quelques millimetres de longueur, que les paleoles, 

 les etamines et I'ovaire, ayant la forme d'ecailles, ne sont point distiucts les uns des 

 autres, ces ecailles sont constituees par des cellules naissantes tres-moUes, pulpeuses, qui 

 se laissent penetrer facilement, et c'est a cette epoque que les anguUlules en contact 

 avec rej)i determinent la production de la nielle, en s'introduisant dans leur parenchyme. 

 Mais, lorsque ces ecailles acquierent la forme des diverses parties qui constituent la fleur 

 du ble, lorsque le pistil bifide devient distinct, les auguillules ne penetrent plus dans 

 leur parenchyme, trop consistant sans doute, et la nielle ne pent plus ctre produite; 

 c'est un fait que j"'ai constate par plusieurs experiences" (p. 18). This piercing and 

 occupation of a part of the rudimentary flower arrests its development, though it stimu- 

 lates growth. A gall-like body is more rapidly produced in the site which should have 

 been occupied by the germen, Avhilst the young worms soon become perfectly developed 

 males and females. These vary in number from two to ten or twelve in each gall, and, 

 after producing an enormous number of ova containing fully formed young — which 

 speedily lil^erate themselves, though they afterwards undergo little change — themselves 

 die and wither, at the time when the gall begins to assume its characteristic purplish- 

 brown or l)lack appearance. 



In harmony with this method of infection of the wheat by the Vibrio tritici, as revealed 

 by Davaine, I may state that in several grasses I have found different species of these 

 free Nematodes, lying between the inner sheaths of the leaves, near the bottom of the 

 culm. In Festuca elatior I met with no less than five species in this situation, belonging 

 to the genera Donjlaimus, MonoiicJins, and JPlcctus ; and in the stalks of wheat and oats 

 removed from stubljle-fields I have frequently found specimens either of these genera or 

 of Rhahditis, Aphelenchus, or Cephalobus. In addition to a malady of oats and maize 

 similar to that of the wheat, and said to be produced by the same animal, Steinbuch', 

 nearly a century ago, recognized a disease somewhat similar to the " purples" in two of the 

 bent-grasses {Agrostis) ; and, from the frequent presence of these Nematoids in the situation 

 named, I suspect such diseases of grass will be found more frequent, if specially looked 

 after. As another instance of disease induced in plants by these animals may be men- 

 tioned the discovery of Ivuhn-, who has ascertained that a long-known and recognized 

 disease of the common teasel {Dip)sacns fullonum) is owing to the presence of a number 



' Naturforsch. xxviii. S. 233, tab. v. ■ Zeitsch. fiir wissen. Zoolog. 1857, t. ix. p. 189. 



